Tapped delay line phase discriminator

ABSTRACT

A phase discriminator comprises a transmission line which is tapped by four detectors connected respectively to four points spaced along the line at regular intervals of lambda /8. The line is tapped by a fifth detector connected to a point on the line separated from one of those four points by lambda /16, lambda being the wavelength of two signals fed to respective ends of the line. This arrangement enables the phase difference to be located within intervals of pi /8 radians. The fifth detector may suitably be situated symmetrically with respect to the first four two further detectors may tap the line at two additional tapping points, one being located lambda /32 from an end tapping-point and the other additional point being 3 lambda /32 from a penultimate tapping-point: this enables the phase difference to be located within intervals of pi /16 radians.

United States Patent To'zer Oct. 23, 1973 TAPPED DELAY LINE PHASE DISCEIMINATOR Appl. No.: 273,346

{30] Foreign Application Priority Data Aug. 3, 1971 Great Britain36,390/71 US. Cl 324/84, 324/188 Int. Cl. G01r 25/02, G04f 9/00 Field ofSearch 324/84, 188

References Cited UNITED STATES PATENTS l2/l963 Preikschat 324/84 XPrimary ExaminerAlfred E. Smith Attorney-Frank R. Trifari [57] ABSTRACTA phase discriminator comprises a transmission line which is tapped byfour detectors connected respectively to four points spaced along theline at regular intervals of M8. The line is tapped by a fifth detectorconnected to a point on the line separated from one of those four pointsby )t/l6, A being the wavelength of two signals fed to respective endsof the line. This arrangement enables the phase difference to be locatedwithin intervals of 1r/8 radians. The fifth detector may suitably besituated symmetrically with respect to the first four two furtherdetectors may tap the line at two additional tapping points, one beinglocated M32 from an end tapping-point and the other additional pointbeing 3A/32 from a penultimate tapping-point: this enables the phasedifference to be located within intervals of 1r/l6 radians.

5 Claims, 7 Drawing Figures L a a 4 a m abl/l U TAPPED DELAY LINE PHASEDISCRIMINATOR This invention relates to phase discriminators of the typecomprising a transmission line tapped by detectors at various pointsalong the line, the two signals whose phases are to be compared beingapplied one to each end of the line. The term transmission line orbriefly line" in this specification includes waveguide.

A known form of phase discriminator comprises a line 3M8 long, where )tis the wavelength of the signals in the line, tapped by four detectordiodes at points. spaced along the line at regular intervals of M8. Thisarrangement enables the phase difference to be located within aninterval of 7r/4 radians (with a further uncertainty of n.2'n' radians,where n is an integer).

According to the invention a phase discriminator, for

comparing the phases of two signals, comprises a transmission line whichis tapped by four detectors connected one to each of four points spacedalong the line at regular intervals of M8, and which is tapped by afifth detector connected to a point on the line separated from any oneof those four points by an interval of M16, A being the wavelength ofthe signals in the line. Suitably, the fifth tapping-point is situatedsymmetrically with respect to the first four tapping-points; in thiscase, two further detectors may tap the line, one at each point which isM32 from an end tapping-point and 3A/32 from a penultimatetapping-point. The phase difference may be located within an interval of11/8 radians with the five-tap line, and within an interval of fir/ l 6radians with the seven-tap line. The latter degree of accuracy may beobtained with arrangements of seven taps other than that mentionedabove. With all arrangements, both fiveand seven-tap, there is always afurther uncertainty of n.21r radians in the phase difference.

In most cases, the transmission line may suitably be 3M8 long; thisgives the most compact arrangement. Spacings greater than 80 /8 betweenthe first four tapping-points could be used, but errors due to slightlyincorrect positioning of one or more of the tappingpoints, or to thesignal wavelength not being exactly the designwavelength, would begreater.

The invention will now be more fully described with reference to theaccompanying diagrammatic drawings, in which: 7

FIG. 1 shows a transmission line tapped by two detectors;

FIGS. 2(a), 2(b), 2(0), show three line according to the invention;

FIG. 3 shows a seven-tap line according to the invention;

FIG. 4 illustrates an embodiment of the form of FIG.

2(b), and

FIG. 5 is a schematical diagram of a phase discriminator employing theline of FIG. 2(a).

Referring to FIG. '5, a line of length L is fed from matched sources S1and S2 at its left-hand and righthand ends with signals represented bya.cos wt and b.cos (wt respectively; a) is the angular frequency and q5is the phase difference between the signals. A standing wave is set upin the line. Referring now to FIG. 1 position along the line is denotedby x, the ends of the line being at x= 0 and x L, and the propagationconstant in the line is g forms of a five-tap The output of a square-lawdetector tapping the line at a point x and assumed not to load the lineappreciably is given by [a b 2ab cos ((1) kL+ 2kx) /2 The output of sucha detector tapping the line at a point x subtracted from that of adetector tapping the line at x,, gives the difference output 2ab sin k(x, x,) sin (4: kL k [x,+ x

The sign of this quantity, with a pair of fixed detectors and signals ofconstant frequency, varies only with the magnitude of d), and thusenables d: to be located within an interval of 11' radians (with thefurther uncertainty of n.21r radians). The sign may be represented by abinary digit, 0 corresponding to sin d) being negative and 1corresponding to sin 4; being positive.

The phase difference may be determined more accurately by obtaining thedifferences in output between various pairs of detectors connected to amulti-tap line. FIGS. 2(a), 2(b), 2(c), show three forms of five-tapline of length 3M8 tapped by four detectors d connected to points A, B,C, D, spaced along the line at regular intervals of M8, and tapped by afifth detector d connected to a point B separated from one of those fourpoints by M16. (The configuration of FIG. 2(c) requires the line to beextended.) FIG. 5 shows the detectors d and a logic circuitry includingsubtracting circuits D-B, D-E, A-B, AE, A-C, B-E, A-D and E-C employedwith the configuration 2(a), and the relative amplitudes of thedifference outputs are shown in Table l; for mathematical convenience,the substitution d) 31r/4 has been made. I

The difference output signals from the subtracting circuits are fed to abinary logic circuitry b which determines by a binary digit 0 or 1 thesign of each signal, producing an eight-bit Johnson code an analogousarrangement of the logic circuitry of this type has been disclosed inthe British Patent Specification No. 1,l9l,83l. This Johnson code isgiven in Table II, and shows how and thereby (I) may be located withinintervals of 1r/8 radians. Tables similar to I and II may be drawn upfor the configurations 2(b) and 2(0). For the configuration 2(0), L"IA/l6 and, therefore, 4) (71r/8). An embodiment with the symmetricalconfiguration of FIG. 2(a) may be advantageous in, for example, thelayout of components.

FIG. 3 illustrates a further form of discriminator having-a total ofseven tapping points, enabling d: to be located within an interval'of1r/l6 radians. The two additional tapping-points indicated by F and Garesituated M32 from an end tapping-point and 3 ./32 from a penultimatetapping-point, namely at x =A/32 and x= Ila/32 respectively. Thedetectors employed and the relative amplitudes of the difference outputsare given in Table III.

The arrangement of FIG. 3 is based on the five-tap line of FIG. 2(a). Onthat basis, other positions for the sixth and seventh taps are possible,but each of the resultant configurations has the disadvantage ofrequiring the use of one or more difference output signals having arelative amplitude of only sin (Tr/l6) 0.195 This will result in a lackof sensitivity and may produce noise problems in the logic circuitryunless the amplitudes of similarly be devised on the basis of thefive-tap lines of T A B L E III FIGS. 2(b) and 2(c). DetectorsPhase-dependent Relative amplitude of FIG. 4 illustrates a suitableembodiment of a line, 2 x: dlffemrnce output difference output tapped atfive points indicated by A,B,C,D,E, and arranged as in FIG. 2(b). Astrip 1 of copper foil is at- 5 g g 2 Ml) Z682? tached to one surface ofa polystyrene sheet 2 com- D sin (6 48) :924 pletely covered on theopposite surface by a first cop- G C s in (0+ 31r/l6) sin 31/ 6) =0-556perfoil ground-plane. The strip l is insulated from a 2 g gig 2) z gffigg;gggz second ground-plane by a dielectric sheet similar to 2, A Esin (0 311/8) sin (31r/8) 0.924 giving a symmetrical disposition. Adiscriminator of 10 i 5 231 74; f iQ g3 this form was found to operatesatisfactorily at 40 MHz. F C Si (9 2, sin (hr/T6) Q 5 B E sin (0 Sir/8)sin (1r/8) =0.383 A K sin (0+ll1r/l6) sin(ll1r/l6)=0.98l TABLE 1 A 0 sina 317/4 sin 30/4) 0.707 F D sin (0+l31r/l6) sin(ll-n'/l6)=0.83l E C sin(0 71r/8) sin (qr/8) 0.383 B K sin (0 l51r/l6) sin (71r/l6) =0.98l

Detectors Phase-dependent Relative amplitude of chosen difference outputdifference output what 5 Clalmed 1s: 1 2 1. A phase discriminator, forcomparing the phases B Sin 0 Sin 1,000 of two signals having awavelength A, D E i (0 +1r/8) i 0-924 comprising, in combination, 2 g 2gTa i figfiggig ggl a transmission line having spaced portions adapted AC sin (0 +1r/2) i (1r/ L000 for receiving said signals, respectively, 2g 23 I 551;435:833; first four tapping points spaced along the line atregu- E C sin (a 7n/8) in (Tr/8) 0-383 lar intervals of )t/S andarranged between said 25 spaced portions, i i a fifth tapping pointspaced from at least one of said first four tapping points by aninterval of A I16, TABLE II detecting means connected to each tappingpoint, 9 A43 and means for providing phase-dependent difference 0signals forming together a code representative of /8 1 1 1 1 1 1 1 v 1the measured phase comprising a logic circuitry in- W 1 1 1 1 1 1 1 oeluding 1 1 1 1 1 1 0 0 subtraction circuits connected between theoutputs 1 1 1 1 1 1 O O 0 of at least eight different pair arrangementsof said 1/2 detecting means. 51/8 1 1 1 1 0 0 0 0 2. A phasediscriminator as claimed in claim 1 3T 1 1 1 0 0 0 0 0 wherein saidlogic circuitry further comprises binary 1 1 0 0 0 0 0 0 circuitsconnected to the outputs of said subtraction 1 0 0 0 0 0 0 0 circuits todisplay at least an eight-bit binary code rep- O o 0 0 0 0 0 0resentative of a measured phase interval. 91r/8 0 0 0 0 0 O 0 1 3. Aphase discriminator according to claim 1 wherein the fifth tapping-pointis situated symmetrilhr/s 0 0 0 0 O 0 1 1 cally with respect to thefirst four tapping-points. 3142 0 0 0 0 0 1 1 1 4. A phase discriminatoraccording to claim 3 and 0 0 0 0 1 1 1 1 tapped by two further detectorsconnected one to each 131/8 0 o 0 1 1 1 1 1 point which is m2 from anend tapping-point and 1r/ 0 0 1 1 1 1 1 l 3A/32 from a penultimatetapping-point. 151r/8 5. A phase discriminator according to claim 1 2T 01 1 1 1 1 1 1 wherein the transmission line is 3M8 long.

7322 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,768,007 Dated October 23, 1973 In nt d/ TIMOTHXCONRAD TOZER It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, line 39, change 80/8 to /8-.

Figure 5, change A" to 3A l6 l6 Signed and sealed this 23rd day of April197L SEAL Attest:

c. MARSHALL DAMN Commissioner of Patents EDWARD MJPLETCHERJR. AttestingOfficer

1. A phase discriminator, for comparing the phases of two signals havinga wavelength lambda , comprising, in combination, a transmission linehaving spaced porTions adapted for receiving said signals, respectively,first four tapping points spaced along the line at regular intervals oflambda /8 and arranged between said spaced portions, a fifth tappingpoint spaced from at least one of said first four tapping points by aninterval of lambda /16, detecting means connected to each tapping point,and means for providing phase-dependent difference signals formingtogether a code representative of the measured phase comprising a logiccircuitry including subtraction circuits connected between the outputsof at least eight different pair arrangements of said detecting means.2. A phase discriminator as claimed in claim 1 wherein said logiccircuitry further comprises binary circuits connected to the outputs ofsaid subtraction circuits to display at least an eight-bit binary coderepresentative of a measured phase interval.
 3. A phase discriminatoraccording to claim 1 wherein the fifth tapping-point is situatedsymmetrically with respect to the first four tapping-points.
 4. A phasediscriminator according to claim 3 and tapped by two further detectorsconnected one to each point which is lambda /32 from an endtapping-point and 3 lambda /32 from a penultimate tapping-point.
 5. Aphase discriminator according to claim 1 wherein the transmission lineis 3 lambda /8 long.